CODEWITHSUNDEEP
python-3.x
esTERY
esTERY

Reputation: 31

Finding an index in a list using 2 lists

Im trying to find the index of each 1 that is at the end of each group(sequence) of 1s. The output for the example below should be [17, 12, 9, 5, 1].

I can find the 1 at index 17 using the formula below but I also need to find the 1 at index 12. (i.e. it's the last instance of 1 in each sequence (or group) of 1s)

list = [1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0]

index_list1 = [i for i, v in enumerate(list) if v == 1] 
index_list0 = [i for i, v in enumerate(list) if v == 0]

val1 = None
for i in index_list1[::-1]:
   if i < index_list0[-1]:
      val1 = i
      break
   else:
      val1 = index_list1[-1]
if val1 is not None:
   index1 = val1

Upvotes: 1

Views: 36

Answers (1)

Selcuk
Selcuk

Reputation: 59184

You can simply use a conditional list comprehension:

my_list = [1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0]
results = [i for i, value in enumerate(my_list) if value == 1 and (my_list+[0])[i+1] != 1]
print(results)

this will print

[1, 5, 9, 12, 17]

The reason to append a [0] is to take care of cases where the original list ends with a 1.

Upvotes: 1

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